"We needn't bother about that," said Frank. "Anything that these people know the intelligence department has found out. No troops advancing at all openly could get by the aeroplanes without being seen. And I think the railroad in this direction has been watched. I saw a lot of aeroplanes flying over this way this afternoon, and there would be more from Boulogne. There are English warships there, I've heard, and their naval flyers would cover this part of the country."

Suddenly Henri slowed down the car. He kept one hand on the wheel, the car moving slowly forward, but his gaze was fixed on the sky. Finally he stopped the car altogether.

"Look up there," he said, quietly, to Frank. "Do you see that light?

First I thought it was a star. But there aren't any other stars, and now I'm sure it's moving. Do you see?"

He pointed, and Frank's eyes followed his finger.

"You're right," he said. "h.e.l.lo! Now it's gone--no, there it is again!

See, it flashes and then disappears! It's some sort of a signal from the air. Keep the car still."

He tried to follow the flashes of the light, hoping to read the message if it was in Morse code. But he soon found that it was not. And then Henri cried out sharply.

"If it's a signal, it's being answered from over there!" he said. "See, there's a light waving there. It looks as if it might be from the roof of a house. I--"

CHAPTER XVI

A DARING EXPLOIT

Frank leaped out.

"Turn the car around first," he said. Henri obeyed. "Now try your starter. Cut out the motor and then see if she starts quickly."

Henri, mystified, obeyed.

"Why?" he asked.

"Because when we want to start, we may have to do it in an awful hurry,"

said Frank. He searched the road for a moment. "Run her back a few feet to where that big tree is. It's darker there than anywhere else around here. All right, that's far enough. We'll have to take the chance of something coming along while we're gone and b.u.mping into her but I don't believe there's much risk of that. Now, come on! And quiet! We've got to get up to that place without being seen."

Cautiously they approached the house. No lights showed in any of its windows; the place looked deserted. Indeed, all around it were traces of hasty flight. It was a wayside inn, of a type common always in France, commoner than ever since the spread of the craze for automobiles and motor touring. Suddenly Frank stopped.

"Wait a minute for me," he said. "I've got to go back to the car. I ought to have thought of it before."

"What do you want?"

"Batteries. I saw a coil of wire in the car and I want that, too. And there must be batteries. A car like this would carry everything needed for small repairs, wouldn't it?"

"Yes. I think you'll find them under my seat."

Frank was back in less than five minutes.

"All right," he said. "I don't know whether we'll have time to do what I want or not, and whether I'll be able to do it, anyhow. But it's worth trying. Now come on past the house. Easy! This is the hardest part of it."

They slipped by. However, Frank uttered a suppressed exclamation as soon as they had done so. Before them, on the right of the road was a field easily two or three times as large as the ordinary French field. As a rule the land in France is split up into very small sections, closely cultivated. But here was a cleared field as large as those commonly seen in England or America, with no fences for perhaps a quarter of a mile in any direction. Henri turned to look back at the inn.

"They're still signalling from there--and look! There are two lights now, instead of one, above!"

These lights were still some distance away. Frank studied them. Then he led the way into the field.

"I thought so!" he said, with suppressed triumph in his voice. "Do you see those barrels over there toward the inn? There's petrol in those--or I'll eat my shirt!"

"And if there is?" said Henri. "What then?"

"Can't you guess? What do you suppose those lights mean?"

"Aeroplanes?"

"Never! They wouldn't flash that way. They'd have to be in a different position entirely. No. Dirigibles!"

"Zeppelins?"

"Perhaps. Perhaps Pa.r.s.evals or Schutte-Lanz airships. I think Pa.r.s.evals, for they need gasoline. And Zeppelins could fly from Brussels or Liege, almost from Cologne--oh, I have it! That's why they need petrol!"

"Why?"

"They haven't flown over Belgium at all! They are from the sea!"

"Oh--so that they could come secretly, and not be seen as they pa.s.sed over Belgium?"

"Yes. If they flew over Belgium they would have to cross some territory that the Germans do not hold, and word would go to Antwerp and from there to the army here. Now quickly! They will be here soon. They are coming nearer every minute."

They went to the barrels as fast as they dared. There was nearly a score of them, all close together. Each had a tap, and it was proof enough that they contained petrol to open the tap of one. The smell identified them beyond any doubt whatever.

"Come on, and help me dig a hole," said Frank. He dropped to his knees, and began scooping out the soft earth with his hands. Henri fell to with a will, though he was sadly puzzled. But when the hole had been dug to a depth of perhaps two feet, and Frank began to hollow out a trench toward the barrels he began to understand. And as soon as he did, he worked as hard as Frank himself, careless of torn finger nails and bleeding hands.

They carried the trench to the foot of one of the barrels, and Frank turned the tap. The gasoline ran out into the trench, and flowed to the hole. Frank ran back to the hole.

"Stop it when I give the word," he said. "Now!"

Then he was busy with the copper wire he had brought from the automobile for several minutes. The wire had been carried either to repair cut telegraph or telephone wires, or to serve as the conductor for a field system of lighting. But whatever its original purpose had been, Frank was thankful now that he had found it. He worked fast, and was satisfied at last.

"Now a little straw and a few twigs over the hole and the trench--and the sooner they come, the better!"

"Yes, the sooner, the better!" echoed Henri, tremendously excited, now that he understood, even if rather vaguely, what Frank planned. "Vive la France! A bas les Allemands!"

As they went back toward the road Frank trailed the wire behind him in two lengths. And when they reached the road, he dropped into the ditch, and was busy for some minutes.

"Now if it only works!" he said. "Perhaps it will; perhaps it won't. But it can't do any harm. That's certain."

"They're coming closer. I think I can see their shapes now--and there are two of them," said Henri. "Do you see?"

For a moment Frank could not. Henri's eyes were sharper than his. But then he did make out vaguely two immense shapes that were coming through the air. Soon, too, the faint hum of their powerful motors made itself heard.

"Zeppelins and big fellows, too," said Frank. "All the better!"